How to make a folder can't be deleted and be modified folder name. But you can still add files in it?

Question

I want to make a shared disk with people online using ubuntu VPS. So as the title says, I want to make a folder can't be deleted and be modified folder name. But you can still add files in it (it's better if only can add files in it, but can't modify files and delete files init) .

I've tried chmod and chattr ways, but seems like both of them can't 100% meet my needs.

Sorry if my poor English caused some inconvenience.

Answer 1

let's use /tmp/some/path as an example. You create /tmp/some and /tmp/some/path as e.g. root, and change permissions on /tmp/some/path to allow write for everyone:

merlin@uc-s4m75657:~$ sudo mkdir -p /tmp/some/path
merlin@uc-s4m75657:~$ sudo chmod 0777 /tmp/some/path
merlin@uc-s4m75657:~$ ls -l /tmp/some/
итого 4
drwxrwxrwx 2 root root 4096 июл 28 11:17 path
merlin@uc-s4m75657:~$ ls -l /tmp/some/path/
итого 0
merlin@uc-s4m75657:~$ rm -rf /tmp/some/path
rm: невозможно удалить '/tmp/some/path': Отказано в доступе

(my locale is russian; "итого" means "total", "Отказано в доступе" is "Access denied")

That's all. Let's check. Since everything is owned by the root, ordinary user can't do anything with /tmp/some, including renaming or removal of /tmp/some/path, because it's path item of /tmp/some directory where this user isn't given any access besides read and list.

However, user is allowed to create items under /tmp/some/path because we given the permission to do it:

merlin@uc-s4m75657:~$ mkdir /tmp/some/path/1
merlin@uc-s4m75657:~$ touch /tmp/some/path/2
merlin@uc-s4m75657:~$ ls -la /tmp/some/path
итого 12
drwxrwxrwx 3 root   root   4096 июл 28 11:18 .
drwxr-xr-x 3 root   root   4096 июл 28 11:17 ..
drwxr-xr-x 2 merlin merlin 4096 июл 28 11:18 1
-rw-r--r-- 1 merlin merlin    0 июл 28 11:18 2
merlin@uc-s4m75657:~$ mv /tmp/some/path/1 /tmp/some/path/3
merlin@uc-s4m75657:~$ ls -la /tmp/some/path
итого 12
drwxrwxrwx 3 root   root   4096 июл 28 11:19 .
drwxr-xr-x 3 root   root   4096 июл 28 11:17 ..
-rw-r--r-- 1 merlin merlin    0 июл 28 11:18 2
drwxr-xr-x 2 merlin merlin 4096 июл 28 11:18 3

---

Unfortunately, you can't really set distinct "create", "rename" and "remove" permissions on objects in Linux filesystems. This is the property of all POSIX-compartible filesystems actually, even if you try to use POSIX ACL. Users who created objects will be their respective owners, and will be able to do anything while the permissions on /tmp/some/path allow them to write to that directory. Creation, removal and renaming are all controlled by a single flag both in traditional Unix modes and in POSIX ACL.

So allowing to create items but preventing their subsequent removal is impossible in Linux. This is one of the few places where POSIX standard completely sucks and Windows has much more versatile permission system.

Answer 2

The sticky permission in Linux is a solution for you. This make a folder contents (files, subfolders, ) to stick to the folder and can be removed or renamed only their respective owner or the root.

Here is how to appy it on your folder /tmp/some/path

$ chmod +t /tmp/some/path

This adds to any other rwx permissions.